1. Field of the Invention
This invention relates generally to the fabrication of composite structures. More particularly, the invention pertains to apparatus for applying shrink wrap and/or other tape or tape-like materials to a composite structure formed on a tooling mandrel or the like.
2. State of the Art
Composite reinforced structures are typically useful where light weight and strength are required, and include such items as shrouds, casings, shafts, tanks, airfoils and fuselage panels in the aerospace technology. It is recognized that composite structures would be useful in many other applications, were it not for the relatively high cost. One item of significant expense in producing composite structures is found in the step of applying an overwrap release material to the uncured composite structure and/or the tooling. In the manufacture of composite structures by winding of fiber tows on a mandrel or other tool, a layer of release material may be first placed on the tooling, fiber placement/winding is performed, and the fiber-wound tool is cured to harden the component before removing it from the tooling. Use of an overwrap material which easily releases off component surfaces, or, if so used, the tool, permits ready consolidation of the uncured composite structure, or, if so used, easy separation of the component from the tool, following curing. A shrink-wrap overwrap material is used to facilitate the consolidation of the composite structure during the curing process by the shrink-wrap material exerting a force on the composite structure due to the heating and attendant shrinkage of the shrink-wrap material, typically the composite structure being cured in an autoclave. In the case of the tool, it is very important that none of the resin of the composite component touches the mandrel surface and adheres thereto because removal of the product from the mandrel is made difficult. Typically, shrink-wrap materials, such as a suitable shrink-wrap plastic material, or release materials such as paper or a non-adhering film of plastic, such as polyethylene, have been or are applied, in sheet form or other suitable forms, to the tool by hand. The shrink-wrap materials and release materials have also been produced and applied in the form of a tape.
In a typical process of overwrapping, an operator holds a spool of tape in a gloved hand and, with the other hand, guides the tape onto the composite structure or a rotating mandrel, letting it wrap itself around the composite structure or mandrel while attempting to manually maintain constant tape tension and tape advance.
Several deficiencies in this method are obvious. First, the operator must simultaneously control the continuously changing advancing placement of the tape on the composite structure or mandrel and continuously attempt to keep as constant tension as possible on the tape. Even if the mandrel is rotated at a slow speed, tape application will not be uniform in each instance, nor uniform from one composite structure or mandrel to the next. The manual application requires a high degree of mental concentration of the operator and a high degree of manual dexterity of the operator, and a brief lapse of either may require rework of an overwrap, which may be difficult. Even highly qualified personnel may produce defective overwrapping of composite structures, mandrels, or tools, leading to irregularities in the finished surface of the finished product. Such defects include irregular overlapping of layers, varying thicknesses, voids, etc. and are particularly prevalent in products of complex geometric shapes.
Each unit of composite structure product fabricated by fiber placement or winding process on a mandrel or other suitable tooling can have a shrink-wrap material applied thereover at the end of the placement or winding process to help consolidate the uncured fiber forming the composite structure during the curing thereof in an autoclave. Winding shrink-wrap material over the uncured composite structure is a relatively lengthy, time-consuming process. The length of time for the winding of the shrink-wrap material over the uncured composite structure increases with the geometric shape and size of the composite structure. Large and complex shaped geometric structures require greater winding time than small, simple geometric structures.
Similarly, each unit of composite product fabricated by fiber placement/winding on a mandrel requires an initial overwrapping of the tooling, e.g. mandrel, with a release material, prior to fiber placement/winding. The time for overwrapping is relatively lengthy, particularly for tooling of complex geometric shape.
A great deal of effort has been expended in the development of fiber placement/winding machines, as characterized in U.S. Pat. Nos. 4,872,619, 4,877,193, and 4,907,754 of Vaniglia, U.S. Pat. No. 4,943,338 of Wisbey, U.S. Pat. No. 5,045,147 of Benson et al., U.S. Pat. No. 5,290,389 of Shupe et al., and U.S. Pat. No. 5,472,553 of Roberts.
However, the wrapping of uncured composite structures and/or the overwrapping of tooling with shrink-wrap materials or release materials, respectively, has generally remained as a manual process, particularly for uncured composite structures and/or tooling for composite structures of complex geometric shape.
In U.S. Pat. No. 4,938,824 of Youngkeit, a method for forming and applying composite tape to a mandrel is described. The composite tape is formed by fiber winding on a mandrel covered with xe2x80x9ca suitable backing film or paper (not shown) such as, for example, polyethylene, nylon, or another suitable plastic film on the mandrel . . .xe2x80x9d There is no mention of how the backing material is placed on the mandrel. In this reference, the composite material on the mandrel is subsequently cut into strips for subsequent application in tape form to a product mandrel, and the backing material is retained on the backside of the composite tape during intermediate storage on reels.
There is a need in the art for an apparatus capable of automated placement of one or more tapes of overwrap material on tooling, such as a rotatable mandrel.
There is a need for such an apparatus which may be readily adapted to control by existing automated machines at a composite manufacturing site, thereby avoiding the high cost of additional computer manipulable, multi-axis machines, computer programming, and hand placement of wrapped materials. Particularly, there is a need for such an apparatus for the wrapping or winding of shrink-wrap materials over an uncured composite structure to replace the hand application thereof presently occurring.
Furthermore, installation of a separate machine for the wrapping of shrink-wrap material over an uncured composite structure or the overwrapping of a mandrel or other tooling will include a carriage of a size which may require a separate station for overwrapping. Thus, it would be necessary to physically transfer the uncured composite structure to another station where the machine is located for the wrapping of the shrink-wrap material after the wrapping of the shrink-wrap material or the transfer of the mandrel from an overwrap station to a fiber placement station after an overwrapping step, such use of a separate machine for such wrapping being undesirable from a process standpoint, a facilities standpoint, and a cost standpoint.
Therefore, it is very desirable to have an apparatus which may be attached to an existing multi-axis fiber placement/winding machine after the completion of the fiber placement/winding to form the uncured composite structure or prior to the formation of the uncured composited structure on a mandrel or other suitable tooling, the apparatus being used for the wrapping of shrink-wrap material over the uncured composite structure or the overwrapping of the mandrel or other suitable tooling before the formation of the uncured composite structure thereon.
The invention comprises a multi-spool overwrap tape material end-effector apparatus which is attachable on multi-axis fiber placement machines. The end-effector apparatus is useful for placing shrink wrap material on uncured composite structures having a complex geometric shape of any size and other overwrap materials, such as release agents, for example, on mandrels or suitable tooling of complex geometry of any size, or the interior thereof. The end-effector apparatus is lightweight, i.e. may be manually lifted, and is readily attached to and detached from a multi-axis fiber placement/winding machine of the type disclosed in U.S. Pat. No. 4,867,834, i.e. a 6- or 7-axis, or any desired number axis, multi-axis fiber placement/winding machine.
In the end-effector apparatus of the invention, shrink-wrap materials, overwrapping tapes, and/or any other desired materials are dispensed from at least one spool, but preferably three or more spools, under tension to a guide roller or redirect roller and then to an application roller for application of the tape(s) to un uncured composite structure, a mandrel, or any other suitable tooling. Each channel of tape application is independently controlled with respect to unspooling tension, and the unspooling speed is dependent upon the mandrel shape and turning speed (RPM). Control of the fiber placement/winding machine permits delivery of the tape or tapes either upon the uncured composite structure, the mandrel surface, the surface of the other suitable tooling, or at a standoff distance from any of such. A sensor arm serves several purposes. First, the arm senses the diameter of the tape spool for controlling the tension placed on the unspooling tape. Second, the arm also prevents the tape from excessive unwinding, e.g., when the apparatus is inverted.
The end-effector apparatus of the invention provides a short, simple, direct, non-convoluted tape delivery path from each tape spool to the delivery roller, promoting reliable operation and precise control of tape placement onto the tooling, as well as facilitating precise termination and re-start of tape placement.
The end-effector apparatus of the invention provides for very consistent and controlled wrapping of uncured composite structures with shrink-wrap material or overwrapping of mandrels or other suitable tooling with a suitable release material. Composite structures which have consistently smoother, more even surfaces are produced using the end-effector apparatus of the present invention. Voids are generally eliminated and ply compactions and consolidations of the fiber materials are more consistent and repeatable than in hand-applied overwraps.
Processing time of the formation and curing of the composite structure is also reduced because of the automated operation of the end-effector apparatus and because of the simultaneous, multiple tape applications in a preferred embodiment of the apparatus.